We could do an SSTO today with a lot of money, but it wouldn't get a lot there. 11 tonnes is virtually no payload.

11 tonnes is larger than most payloads launched today... its enough to put about four tonnes into GTO, which is large enough for a reasonably-sized commsat. The Delta Clipper would have serviced most of today's market for payloads. Its also a perfectly decent size for an orbital tourism or passenger vehicle.

I'll certainly concede that lunar or Mars spacecraft can't realistically be built from 11-tonne pieces, even if one felt that orbital assembly was reasonable in the first place. But something like the Delta Clipper would still be very useful to have... and, I think, a more important development than a human return to the Moon.

An aside - in 'Case for Mars', Zubrin actually outlines a plan for doing a Mars mission entirely with Delta Clipper class SSTOs - it requires orbital refueling, so was considered somewhat futuristic. Still interesting though.

There is no way, I think, that an ssto could compete economically with itty bitty throw away launchers, especially when the likes of Space-X get going.

Difficulty and cost vs. payload size is an exponential relationship so the pay-off of reusables doesn't kick into until you get up large.

What makes re-usables so hard is not their technical feasability (well partly it is) because they are theoretically possible, and so eventually engineeringly possible, but because of ecconomic barriers.

1) Nasa never has enough money in one place to really go for it.
2) It might turn out to be harder than we think, thus the money risked is lost if more cannot be found to fund through to completion
3) The opportunity cost is so high - the same money but into throw away mega-launchers could but a darn sight more payload into orbit. You have to want to put up a whole lot of stuff to beat out economies of scale with margins of advantage that thin.

I dont really understand this quest for a SSTO RLV, why do we need to make life so difficult for ourselves? Undoubtedly these things will come but lets get the flight rate up first and generate more opportunities for space business. Nothing wrong with expendable boosters if they are cheaper than an RLV

A small RLV on top of a cheap throw away booster would be good for crew flights and do the job just as well as a totally reusable craft and give an advantage in payload due to staging. NASA's original shuttle concept or the HL-20 would have been much safer, less complicated and more reliable for crew transportation.

_________________A journey of a thousand miles begins with a single step.

in one of my posts to Andy Hill's CXV-thread in the Financial Barriers section I calculated the number of flights at which the CXV would be more economical than Soyuz. This number is between 8 and 10.

If the CXV is private and NAASA simply is booking flights then the company running the CXV could sell flights to every one else too - to ESA for example and to JAXA. This way the number at which the CXV beins to be more economical than Soyuz would be easyly to be achieved.

All this I already have to work out a little bit but it menas that small reusable vehicles can achieve economic advantages over other vehicles very quickly.

For this reason their technology should be improved and extended beginning now I think.

When people talk about RLV they usually mean SSTO RLV. We do not yet even have any SSTO expendable vehicle. That by itself is a big improvement on current technology. Then making it reusable is another giant step. We are just reaching too far trying to take these two big steps at one leap.

Maybe I shouldn't have been so strident about the advantages of SSTO or RLVs in general... I don't really know 'the answer', I'm not sure if anyone does, and certainly I don't believe that RLVs or small ELVs or HLLVs will be a 'silver bullet' and create a spacefaring society overnight (or even in a decade).

I'm not an engineer (yet), so I can't really speak for the ease or difficulty of building an RLV, which was really why I started this thread. By some accounts its a long way off, by others it could have been done in the 70s.

Maybe SpaceX and company can fly ELVs cheaply enough to really grow the launch market so that there's a sounder justification for RLVs... but, for a number of reasons, I really think that RLVs have to be the long term solution, simply because of the capabilities they have:

I can't see a truly robust transportation infrastructure emerging without these characteristics.

Andy Hill wrote:

A small RLV on top of a cheap throw away booster would be good for crew flights and do the job just as well as a totally reusable craft and give an advantage in payload due to staging.

Hmm - I'm fairly convinced by the rationale which says that if you're going to reuse a stage, make it the first stage. I've never heard anybody argue that we're not technically ready to build a reusable first stage. Then again, I know that manned spacecraft are very expensive, and since you have to get the occupants back to Earth somehow in any event, that might be an exception.

campbelp2002 wrote:

We do not yet even have any SSTO expendable vehicle. That by itself is a big improvement on current technology.

Wasn't there a thought experiment that said sticking a few SSMEs on the ET would make an SSTO ELV with a significant payload?

Wasn't there a thought experiment that said sticking a few SSMEs on the ET would make an SSTO ELV with a significant payload?

I don't know, but in any case I don't care about thought experiments. We do not have any operational launch vehicle that takes it's payload all the way to orbit without dropping any parts off. Such a vehicle would be an expendable SSTO vehicle if it had no capability for deceleration and intact reentry. It could probably be built pretty easily right now, but the payload would be much reduced compared to a similar size two stage rocket. Nobody in his right mind is going to make a one stage rocket that puts a much smaller payload in orbit than a similar size two stage rocket just to say they did it with one stage. I think SpaceX has the right idea in trying to recover both stages of their two stage rocket. A fully reusable 2STO rocket will still have good payload to orbit, and if, as Musk says, the reentry and recovery hardware do not add much weight, then this is really the best way to go. After that has been perfected and operational for some time, then parachute recovery can be replaced with computer controlled fly back to well defined landing areas. Perhaps, eventually, we could even have the first stage fly back to the launch site. Then we would have an almost airline like operation.

1.) most of it is wrapped up fighting a stupid war and
2.) the Air Force and the Navy underspend on space
-- while blowing mega bucks on un-needed fighters, DDX programs and other platforms that would have been fine over Mig Alley or at Scapa or Jutland--but are of little or no use today. JSF cannot down ICBMs, and are not needed to shoot rogue airliners down.

I can do that with a sidewinder-equipped Spad.

There is plenty of money for HLLVs and RLVs. If you recall my astro-rocket link--the two work well together. This also according to the last chapters of the book SPACEFLIGHT IN THE ERA OF AEROSPACEPLANES which should be required reading.

The HLLV is to loft large permanent platforms/modules to space to be serviced by RLV transports. But EELV type also-ran comsat launchers of middling capability is what is familiar, and so the HLLV and RLV advocates are ignored or fight each other as the fighter jocks get everything they want budget wise.

I read somewhere that SSTO RLV would be easy if we lived on a planet the size of Venus. It's that last 1 km/s that makes it so hard.

That's why an uneven TSTO is a good solution. Build the SSTO RLV that you would like to be able to. Say 7 km/s delta-V. Make it simple, strong, reliable. Optimize it for vacuum & re-entry/landing.

Then build a big dumb VTVL RLV first stage that can get to 60 or 70 km doing 1000 m/s at a 45 degree angle. Give it a big wide nose cone that opens up like petals to release the second stage in near-vacuum, then act as drag enhancers/stabilizers for re-entry. It's re-entry won't require much thermal protection, and it will land only 200 to 300 km down range. Barge it, or re-fuel & fly it back to the launch site.

The orbiter sits in a cradle on the first stage, protected from the atmosphere. You can also launch a vacuum-optimized expendable second stage the same way.

If your RLV orbiter is also VTVL, modified versions could be used to land on the Moon or Mars, then launch again.

Give it a big wide nose cone that opens up like petals to release the second stage in near-vacuum, then act as drag enhancers/stabilizers for re-entry.

The big nose cone would be interesting, but unless the majority of your initial payloads are unstreamlined it would probably mass too much to be really worth it. Not that it couldn't be done but it would eat too much into your initial payload (the fueled orbiter) mass. A more elegant approach would be to do it the other way round. Initially you use a streamlined orbiter and attach smaller petals to the first stage. As you said, the petals would slick the craft up during launch and later add enough drag to slow the first stage and assure a tail-first drop.

If at a later date you want to launch unstreamlined orbiters, you could either build a modified first stage with a full shroud or possibly use a disposable shroud for the orbiter. The latter is likely to be lighter as well.

Give it a big wide nose cone that opens up like petals to release the second stage in near-vacuum,

Would a flower-petal nose cone be a better approach than an expendable fairing? Still, like the idea in general very much (though what do I know) - I guess this is the 'Rocket Company' approach again. I'm getting that book for my birthday in two weeks - looking forward to that.

What about applying the titled question of this thread to Mars? How hard is it to develop and construct a reusable vehicle for Mars? Because of all the past and future Mars missions this question appears interesting to me.

There already is work on Methane engines on Earth and even the unar lander by Micro Space has been said to be appicable on Mars.

There is Methane on Mars or it could be produced there. LOX/LH2 might be applied as well.

I recall reading that the X-33 could make orbit if it was launched from Mach 2, instead of merely reaching Mach 15. Mach 2 can be done with mere jet engines. Ideally, it should be SSTO, but TSTO could work if the first stage was good enough.

I think the prime reason why the NASA (and the others) stick to what they know is simply politics. Even the last few NASA guidelines from the congress explicitly state that they should use all the components and infrastructure available right now, instead of developing something new. Because the companies involved are into a good thing that pays really well, and they spend part of that on lobbying.

The most profound decision was to leave LEO and ISS refueling flights to private companies whenever possible (and sponsoring them), because they understand that that is the only way to get things changed.